Medical diagnostic imaging and scanner systems such as magnetic resonance imaging (MRI) apparatus, X-ray machines, positron emission tomography (PET) scanners, and computer tomography (CT) scanners are well known. Such machines are quite popular as a tool for providing images of internal portions of patients for diagnosis of medical conditions, such as internal injuries, cancerous tumors and the like. Owing to good quality tomographic images with low dosage X-ray radiation, the CT scanner has become especially well accepted by the medical profession for examining patients and diagnosing medical conditions.
An annular gantry normally supports many of the components of a CT scanner and includes an outer ring secured to a stand and an inner ring mounted for rotation within the outer ring. During a scanning procedure, a pallet of a patient table is extended through the center of the gantry and the inner ring is rotated about the pallet. A patient lies on the pallet within the center of the gantry during the scanning procedure. The components supported by the gantry can include an x-ray tube for providing the x-ray beam, one or more high voltage power supplies, balancing weights, a data acquisition module, and a bank of detectors diametrically opposed from the x-ray source. At least some of these components are secured in the inner ring for rotation therewith.
In order to obtain tomographic images of a patient with a CT scanner or X-ray CT apparatus, it is necessary that the patient be located exactly at a predetermined position inside the opening of an annular scan gantry of the apparatus. For this reason, such apparatus has been provided with a patient handling couch or table which has a table assembly that is moveable vertically to be in line with an axis of rotation of the scan gantry (such that a longitudinal center line of the patient table is in alignment with the axis of rotation of the scan gantry), and a pallet that supports the patient and is moveable horizontally, or axially in and out of the scan gantry, parallel with the axis of rotation.
Tomotherapy is a new way to deliver radiation treatment for cancer. It delivers a very sophisticated form of IMRT, or intensity modulated radiotherapy, and integrates treatment planning, patient positioning, and treatment delivery in one system. Radiation is one of the most effective cancer treatments available. It works by damaging the cells it strikes: when the cancer cells are damaged enough, they will die. But what happens to healthy cells that are struck by the radiation beam? The key factor for radiotherapy is that healthy cells can repair themselves better than cancer cells. That's why radiotherapy treatments are divided into many treatments, or fractions, over several weeks. Delivering a little radiation to the tumor area every day gives healthy cells time to recover between each session, while causing unrepairable damage to more and more cancer cells.
Radiation treatment is also usually directed at the tumor from several different directions, so that more radiation is targeted on the tumor, but a lesser dose is spread over the surrounding healthy tissue. Even though normal tissue can recover from exposure to radiation, there are often side effects, and of course too much radiation can damage normal tissue beyond repair. Until recently, it was very difficult for doctors to deliver enough radiation to kill a tumor without causing painful or debilitating side effects. Some side effects might go away once the treatment is complete, but others could continue to affect quality of life for years.
Of course, one of the goals of any radiation therapy is to avoid healthy tissue as much as possible, but some healthy cells will be damaged by the radiation treatment. So doctors and scientists have begun to look for better ways to deliver enough radiation to the tumor, while sparing normal tissue as much as possible. One of the most promising methods is IMRT, or intensity modulated radiotherapy.
IMRT is one of the most important recent advances in radiation therapy. The goal of IMRT is to change (modulate) the size, shape, and strength of the radiation beam in order to focus enough dose on the tumor to kill the cancer cells, while sparing as much as possible the surrounding healthy tissue. There are different ways to change the size, shape, and strength of the radiation beam. For example, custom radiation filters called compensators can be used to modulate the radiation beam. But compensators are costly and time-consuming to make, and involve very complicated setup and delivery procedures.
A more promising device for IMRT is called a multileaf collimator, or MLC, which is a device that is attached to the linear accelerator. An MLC is made of many individual fingers or leaves, which move across the beam in a specified pattern to block or allow the passage of radiation, shaping the beam as it is emitted.
Like conventional radiotherapy, conventional IMRT is usually delivered from several different directions (usually 5 to 9, although sometimes as many as 13). The greater the number of beam directions, the more the high dose will be confined to the tumor, and the less chance for debilitating side effects. But conventional IMRT requires a lengthy and complicated setup process for each treatment fraction, and more beam directions requires more time for each treatment fraction.
The Hi-Art system, which has been developed by TomoTherapy™ Inc. of Madison, Wis. in association with the Tomotherapy Research Group of the University of Wisconsin, Madison, takes IMRT one step further, combining a very sophisticated MLC with a unique helical delivery pattern in order to deliver precise radiation at the target. Instead of delivering radiation from just a few directions, the Hi-Art system delivers radiation from every point on the helix, in about the same amount of time as conventional IMRT.
The TomoTherapy Hi-Art System combines treatment planning, patient positioning, and treatment delivery into one system, in order to deliver precise treatment doses without increasing the radiation deposited on healthy tissue. Before beginning tomotherapy treatment, the doctor uses 3-D images (for example, from a computed tomography (CT) scanner) and special software to establish the precise contours for each region of interest (tumor) and any regions at risk (sensitive organs or structures). The doctor decides how much radiation the tumor should receive, as well as acceptable levels for surrounding structures. Then the Hi Art system calculates the appropriate pattern, position, and intensity of the radiation beam to be delivered, to match the doctor's prescription as closely as possible.
The Hi-Art system will allow doctors to take a special CT scan just before each treatment, so they can verify the position of the tumor, and adjust the patient's position if necessary to make sure the radiation is directed right where it should be. The Hi-Art system combines IMRT with a helical (or spiral) delivery pattern to deliver the radiation treatment. Photon radiation is produced by a linear accelerator (or linac for short), which travels in multiple circles all the way around the gantry ring. The linac moves in unison with a device called a multileaf collimator, or MLC. The computer-controlled MLC has two sets of interlaced leaves that move in and out very quickly to constantly modulate the radiation beam as it leaves the accelerator. Meanwhile, the couch or patient table is also moving, guiding the patient slowly through the center of the ring, so each time the linac comes around, it's directing the beam at a slightly different plane.
What is still desired, however, is a new and improved patient table for use with medical diagnostic imaging and scanner systems, such as tomography scanners, and medical treatment systems, such as radiation therapy systems. In particular, what is desired is a patient table including a longitudinally extending pallet having opposing ends that are each laterally adjustable. Among other features and advantages, the new and improved pallet will allow a patient lying on the pallet to be correctly positioned in medical diagnostic and medical treatment systems in a comfortable manner, and without being moved on the pallet. Such a new and improved pallet is particularly desirable for use with a radiation therapy system, such as the TomoTherapy Hi-Art System for example.